Trailers have been around for many years, yet every summer and winter one can observe the owners of boats and snowmobiles, respectively, backing up those devices on trailers with great difficulty. The problem arises from the fact that a trailer being backed-up is an inherently unstable system. A trailer being pushed wants to turn around and be pulled (i.e., to jackknife) instead. To compensate for this instability, the driver must skillfully alternate the direction of his steering so as to cause the trailer to want to turn around and be pulled from opposite sides thereby repeatedly crossing the centerline of the pushing vehicle. Various innovations have been introduced to address this problem in whole or in part. Prior art reveals several attempts to address the problems associated with backing a trailer. The simplest solutions address parts of the problem ranging from ways of sensing the angle of the hitch (see: Kollitz, U.S. Pat. No. 4,122,390), to sensing and displaying the angle of the hitch (see: Gavit, U.S. Pat. No. 3,833,928), to sounding an alarm when a jackknife condition exists or is imminent (see: Kimmel, U.S. Pat. No. 4,040,006). While these solutions are helpful, they only each address a part of the backing problem. Shepard in his U.S. Pat. No. 7,715,953 teaches a complete working system. However, in that teaching, some new needs arise that are addressed by the teaching of the present invention, such as how to install a complete working system as an after market product that can easily be installed or removed and how to install a sensor for measuring the angle formed between the centerline of the vehicle and the centerline of the trailer (i.e., the hitch angle sensor or, as it is sometimes also known, the articulation angle sensor) such that it does not interfere or collide with the trailer tongue or any other parts of the hitching system. In particular, an angle sensor is needed that can get its measurement in-line with the axis of rotation of the trailer tongue upon the hitch ball (i.e., to measure the articulation angle of this hitch joint) without actually being located at that axis of rotation. This hitch angle sensor, in particular, must be designed not to be damaged either during hitching up a trailer (due to a collision between the hitch and sensor with a part of the trailer) nor while towing on the highway (due to kicked up debris).
Trailer guidance systems such as the portable system disclosed in U.S. Patent Application 62/020,526, by Shepard titled “PORTABLE TRAILER GUIDANCE SYSTEM” that was filed on Jul. 9, 2014 require sensors for detecting the hitch angle and the turning radius and output means for displaying the intended trailer destination. Most vehicles do not have integral turning sensors and most trailers and/or hitches do not have integral hitch angle sensors. A solution is to make a hitch angle sensor that can be added to an existing vehicle that did not have such capability leaving the automotive assembly line. Once such an investment in a hitch angle measurement sensor is made, it is possible to leverage this sensor for not only measuring the angle of the hitch, but to also adapt the angle measuring mechanism of the hitch angle sensor to create a guidance mechanism to assist a driver in backing up the vehicle in order to couple the vehicle to the trailer.